Organic blend additive useful for inhibiting localized corrosion of equipment used in oil and gas production

ABSTRACT

An organic blend chemical additive comprising more than 50 wt. % organic solvent (e.g. methanol and/or ethylene glycol), less than 10 wt. % water, a nitrate salt, a maleic acid copolymer, and optionally an imidazoline may be delivered to a production well through a conduit having a stainless steel and corrosion resistant metal alloy surface, such as a capillary string or an umbilical tubing, the organic blend chemical additive being shown to be useful in inhibiting localized corrosion of and improving the repassivation of the equipment or conduit.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit of Provisional Patent ApplicationNo. 62/734,752 filed Sep. 21, 2018, which is incorporated by referenceherein in its entirety.

TECHNICAL FIELD

The invention relates to the use of an organic chemical blend additiveto inhibit corrosion in oil and gas production applications, and moreparticularly relates to using such an additive for inhibiting localizedcorrosion of chemical injection equipment used in the production of oiland gas.

BACKGROUND

It is well known that steel and alloy made tubulars and equipment usedin the production of oil and gas are exposed to corrosive environments.Such environments generally contain acid gases (CO₂ and H₂S) and brinesof various salinities. Under such conditions, the steel or alloy willcorrode, possibly leading to equipment failures, injuries, environmentaldamage, and economic loss.

While the rate at which corrosion will occur depends on a number offactors, such as the type of metal or alloy, partial pressure of theacid gases, salinity, pH, temperature, etc., some sort of corrosionalmost inevitably occurs. One way to mitigate this problem is tointroduce corrosion inhibitors in the hydrocarbon production system.

Corrosion inhibitors are widely introduced into oil and gas productionwells and pipeline transmission lines to help prevent or reducecorrosion of carbon steels surfaces coming into contact with fluids orgases produced from wells.

Methanol-based organic blends containing corrosion and scale inhibitorsare sometimes delivered to production fluids or gases through capillarystrings and umbilical tubing to aid in reducing or preventing corrosionof or formation of scale upon carbon steel surfaces in the well thatcome into contact with the production fluid or gas. However, the use ofsuch methanol-based organic blends, because of the presence ofchlorides, have been shown to generate pitting corrosion of (i.e.localized corrosion) and to reduce the repassivation ability of thestainless steel (e.g. 316L) and corrosion resistant alloy (e.g. Duplex2205) capillary strings and umbilical tubing that are being used todeliver chemicals into the production well.

It would be advantageous to develop an organic chemical blend additivethat would help to inhibit this localized corrosion of the stainlesssteel or corrosion resistant alloy made capillary string and umbilicaltubing while still being useful to inhibit corrosion of and reduce scaleformation upon other metal surfaces in a production well.

SUMMARY

There is provided, in one form, a method of inhibiting corrosion upon ametal surface of equipment used to deliver additives into a productionwell in which an organic chemical blend is introduced to the wellthrough a conduit, such as a capillary string or umbilical tubing, theorganic chemical blend additive being made up of a nitrate salt, amaleic acid copolymer, greater than 50 wt. % of an organic solvent,other organic components and less than 10 wt. % water and the amount ofthe organic chemical blend additive introduced being effective toinhibit localized corrosion of and to improve repassivation potential ofa stainless steel and corrosion resistant alloy surface of the capillarystring or umbilical tubing.

There is also provided, in another non-restrictive form, a treatedsystem containing a conduit for delivering additives into a productionwell having a metal or metal alloy surface, and an organic chemicalblend additive comprising a nitrate salt, a maleic acid copolymer, otherorganic components, greater than 50 wt. % of an organic solvent, andless than 10 wt. % water.

In yet another form, an imidazoline may additionally be included in theorganic chemical blend additive to aid in inhibiting corrosion orimproving repassivation of metal surfaces of equipment and conduits usedto deliver additives into a production well.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a set of graphs comparing the pitting potential, repassivationpotential, and open circuit potential when organic chemical blendadditives having the compositions set forth in Table 1 are applied to aDuplex 2205 alloy surface of a capillary string.

FIG. 2 is a set of graphs comparing the pitting potential, repassivationpotential, and open circuit potential when the organic chemical blendadditives having the compositions set forth in Table 1 are applied to astainless steel 316L surface of a capillary string.

FIG. 3 is a graph comparing the performance of an organic chemical blendadditive that contains both calcium nitrate and a maleic acid copolymerto the performance of an organic chemical blend additive that doesn'tinclude a maleic acid copolymer upon a Duplex 2205 alloy surface and astainless steel 316L surface of a capillary string.

FIG. 4 is a set of graphs comparing the pitting potential, repassivationpotential, and open circuit potential when organic chemical blendadditives having the compositions set forth in Table 2 are applied to aDuplex 2205 alloy surface and a stainless steel 316L surface of acapillary string.

DETAILED DESCRIPTION

As previously noted, metal and metal alloy made conduits, pipes, tubing,and other equipment used to deliver chemicals and additives useful inthe production of oil and gas from a well can experience localizedcorrosion (pitting) from the chemicals being delivered. It has beendiscovered that an effective amount of organic chemical blend additivemade predominantly of an organic solvent containing a nitrate, a maleicacid copolymer, less than 10 wt. % water, and optionally an imidazolinemay be useful to inhibit localized corrosion and improve repassivationof metal and metal alloy surfaces of equipment used to deliver additivesand chemicals to production wells.

The most commonly used equipment for delivering chemicals and additivesto production wells are capillary strings and umbilical tubing. Theseconduits run down to the bottom of the well and the intake point of anelectrical submersible pump to allow for delivery of chemicals andadditives to the fluid in the well. Often, these pieces of equipment aremade from stainless steel, such as 316L, or corrosion resistant alloys,such as Duplex 2205, but are not necessarily limited to these specifictypes of metal or metal alloys.

In one embodiment, the organic chemical blend additive contains orincludes a nitrate salt, a maleic acid copolymer, greater than 50 wt. %of an organic solvent, and less than 10 wt. % water.

Suitable nitrates salts include, but are not limited to, calciumnitrate, sodium nitrate, potassium nitrate, or a combination thereof.Calcium nitrate, in particular, is shown to have better solubility inorganic solvents such as methanol or ethylene glycol.

An example of the maleic acid copolymer that may be used in the organicchemical blend additive is, without limitation, propenoic acid, ethylester, polymer with ethenyl acetate, and/or 2,5-furandione, hydrolyzed.This copolymer is included to aid in the reduction of scale formation inthe production fluid or any metal surfaces in contact with productionfluid. The amount of maleic acid copolymer in the organic chemical blendadditive ranges from about 1 wt. % to about 15 wt. %.

Suitable organic solvents useful in the organic chemical blend additivemay include methanol, ethylene glycol, isopropyl alcohol,2-butoxyethanol, propylene glycol, butyl carbitol, and combinationsthereof.

In one non-restrictive embodiment, the blend is organic-solvent based.That is, the amount of the organic solvent in the organic chemical blendadditive is greater than 50% wt. % and alternatively, greater than 70wt. %, based on the total amount of organic chemical blend additive.Water is present in a small amount, for example, in an amount less than10 wt. %, and alternatively less than 5 wt. %, based on the total amountof organic chemical blend additive.

In one non-limiting embodiment, the amount of nitrate present in theblend ranges from about 0.25% of a 45% aqueous solution of nitrate saltto about 5% of a 45% aqueous solution of the nitrate salt. In yetanother embodiment, the nitrate salt is present in the organic chemicalblend additive in an amount less 2% of a 45% aqueous solution ofnitrate.

In an alternative embodiment, the organic chemical blend additivefurther comprises an imidazoline to help improve corrosion inhibitionand repassivation potential of the metal surface of a conduit used todeliver chemicals and additives to a production well. Imidazolinesuseful in the organic chemical blend additive for this purpose may havethe following general formula:

In this formula, R describes the hydrophobic tail portion of themolecule and P describes the pendant group of the molecule. In oneembodiment, R is a tall oil fatty acid. The pendant group, P, may beselected from a group consisting of (CH₂—CH₂)—X, (CH₂—CH₂—O)_(n)H,CH₂—CH₂—(NH—CH₂—CH₂)^(y)NH—CO—R1, wherein X may be NH₂, OH, or NH—CO—R2,n is 10, and y is equal to or greater than 2. The proportions of theoptional imidazoline in the organic chemical blend additive may rangefrom about 5 wt. % independently to about 30 wt. %.

It is difficult to predict in advance what amount of organic chemicalblend additive should be introduced to the production well to achieve anoptimum corrosion inhibition and repassivation improvement because suchamount is dependent upon many interrelated variables such as, forexample, the nature of the production fluid being extracted from theproduction well, the nature of other the oilfield chemicals beingdelivered, and nature of the metal surface of the conduits and otherequipment used to deliver chemicals to the production well or to carrythe production fluid, etc. Nevertheless, in one non-limiting example,the amount of organic chemical blend additive being delivered rangesfrom about 10 ppm independently to about 1000 ppm independently.Alternatively, the amount of organic chemical blend additive beingdelivered may range from about 50 ppm independently to about 300 ppmindependently or range from about 75 ppm independently to about 150 ppmindependently. The amounts in this paragraph are based on the totalamount of production fluid in the well. As used herein with respect to arange, “independently” means that any threshold may be used togetherwith another threshold to give a suitable alternative range, e.g. about50 ppm independently to about 1000 ppm independently is also considereda suitable alternative range.

For purposes of this disclosure, the term “inhibit” is defined to meanreduce, suppress, or prevent. It is not necessary for the corrosion,localized or general, and scaling of the metal surfaces of capillarystring, umbilical, tubing, or other oil and gas production or pipinghaving metal surfaces to be entirely prevented for the chemical blendadditives discussion herein to be considered effective, althoughcomplete prevention is a desirable goal.

The invention will be further described with respect to the followingExamples, which are not meant to limit the invention, but rather tofurther illustrate the various embodiments.

EXAMPLES

The Cyclic Potentiodynamic Polarization (“CPP”) graphs in FIG. 1 andFIG. 2 depict the pitting potential, repassivation potential, and opencircuit potential performance of organic chemical blend additives havingthe compositions set forth in Table 1 below upon a Duplex 2205 alloysurface and upon a stainless steel 316L surface of a capillary string.Erep−Eocp is the difference between the repassivation potential (Erep)and the open circuit potential (Eocp). The larger the difference inthese values, the more the metal tends to repassivate. An Erep−Eocp>200mV represents an effective protection of the metal surface.

The curves on FIG. 1 demonstrate that an organic chemical blend additivecontaining a maleic acid copolymer, at least 50 wt. % organic solvent,and less than 10 wt. % water, and 0.25% of a 45% aqueous solution ofcalcium nitrate achieves the same amount of corrosion inhibition andrepassivation improvement on Duplex 2205 metal surface as an organicchemical blend additive containing a maleic acid copolymer, at least 50wt. % organic solvent, and less than 10 wt. % water, and 1 or 2% of a45% aqueous solution of calcium nitrate on the same type metal surface.

The performance was a bit different when the organic chemical blendadditive was applied to a stainless steel 316L surface. While anadditive containing only 1% of a 45% aqueous solution of calcium nitrateperformed just as well in inhibiting corrosion and improvingrepassivation potential as an additive that contained 2% of a 45%aqueous solution of calcium nitrate, the results were not as good whenan additive with 0.5% of a 45% aqueous solution of calcium nitrate wasapplied to the stainless steel surface, as shown the curves in FIG. 2.These results indicate that determining what amount of components isnecessary to achieve good results may depend on the stainless steel oralloy used on a given capillary string or umbilical tubing.

In addition, the CPP graph in FIG. 3 indicates that there is asignificant improvement in corrosion inhibition and repassivationimprovement with an organic chemical blend additive that contains boththe nitrate salt and a maleic acid copolymer, Blend B, represented bycurve B as compared to an organic chemical blend additive that doesn'tinclude a maleic acid copolymer, Blend D, represented by curve D. Theseresults suggest that the maleic acid co-polymer may act synergisticallywith the nitrate salt to improve repassivation behavior and inhibitlocalized corrosion.

Table 1 shows the composition of Blends A, B, C, D, and E, the CPPgraphs of which are shown in FIGS. 1, 2, and 3.

TABLE 1 Chemical Blend Additive Compositions Maleic acid copolymer  2-10 2-10  2-10 0.0  2-10 Water <10 <10 <10 <10 <10 Methanol 40-70 40-7040-70 40-70 40-70 Ethylene Glycol 10-30 10-30 10-30 10-30 10-30 45%Calcium Nitrate in water 2.0 1.0 0.25 1.0 0.5 Other Organic compounds10-25 10-25 10-25 10-25 10-25

The CPP graphs in FIG. 4 depict the pitting potential, repassivationpotential, and open circuit potential curves of the organic chemicalblend additives further containing an ethoxylated imidazoline, as setforth in the compositions in Table 2 below, upon a Duplex 2205 alloysurface and upon a stainless steel 316L surface.

TABLE 2 Chemical Blend Additive Compositions-with an imidazolineEthoxylated Imidazoline 10-30 10-30 Maleic acid copolymer  2-10  2-10Water <10 <10 Methanol 40-70 40-70 Ethylene Glycol 10-30 10-30 45%Calcium Nitrate in water 0.0 0.1 Other Organic Components 10-25 10-25

FIG. 4 demonstrates that the addition of an ethoxylated imidazoline tothe organic chemical blend additive, for example, greatly improves therepassivation behavior of Duplex 2205 even when the organic chemicalblend additive contains only 0.1% of a 45% aqueous solution of calciumnitrate, a smaller amount than otherwise employed or expected to achievean Erep−Eocp larger than 200 mV. These results suggest that theimidazoline may act synergistically with the nitrate salt and the maleicacid copolymer to improve repassivation behavior and inhibit localizedcorrosion.

In the foregoing specification, the invention has been described withreference to specific embodiments thereof. However, it will be evidentthat various modifications and changes can be made thereto withoutdeparting from the broader spirit or scope of the invention as set forthin the appended claims. Accordingly, the specification is to be regardedin an illustrative rather than a restrictive sense. For example,metallurgy, equipment, nitrates, maleic acid copolymers, organicsolvents, and other components, falling within the claimed parameters,but not specifically identified or tried in a particular fluid, blend,or method, are expected to be within the scope of this invention.

The present invention may suitably comprise, consist or consistessentially of the elements disclosed and may be practiced in theabsence of an element not disclosed. For example, the method may consistof or consist essentially of introducing an organic chemical blendadditive to a production well via a conduit having a metal surface, theorganic chemical blend additive consisting essentially of or consistingof a nitrate salt, a maleic acid copolymer, greater than 50 wt. % of anorganic solvent, and less than 10 wt. % water. As another example, thetreated system may comprise, consist of, or consist essentially of: aconduit for delivering additives to a production well having a metal ormetal alloy surface; and organic chemical blend additive consistingessentially of or consisting of a nitrate salt, a maleic acid copolymer,greater than 50 wt. % of an organic solvent, and less than 10 wt. %water.

In another non-limiting embodiment, the additive may comprise, consistessentially of, or consist of a nitrate salt, a maleic acid copolymer,greater than 50 wt. % of an organic solvent, and less than 10 wt. %water.

In a different non-restrictive version, the additive may comprise,consist essentially of, or consist of, a nitrate salt, a maleic acidcopolymer, an imidazoline, greater than 50 wt. % of an organic solvent,and less than 10 wt. % water.

As used herein, the terms “comprising,” “including,” “containing,”“characterized by,” and grammatical equivalents thereof are inclusive oropen-ended terms that do not exclude additional, unrecited elements ormethod acts, but also include the more restrictive terms “consisting of”and “consisting essentially of” and grammatical equivalents thereof. Asused herein, the term “may” with respect to a material, structure,feature or method act indicates that such is contemplated for use inimplementation of an embodiment of the disclosure and such term is usedin preference to the more restrictive term “is” so as to avoid anyimplication that other, compatible materials, structures, features andmethods usable in combination therewith should or must be, excluded.

As used herein, the singular forms “a,” “an,” and “the” are intended toinclude the plural forms as well, unless the context clearly indicatesotherwise.

As used herein, the term “and/or” includes any and all combinations ofone or more of the associated listed items.

As used herein, the term “about” in reference to a given parameter isinclusive of the stated value and has the meaning dictated by thecontext (e.g., it includes the degree of error associated withmeasurement of the given parameter).

What is claimed is:
 1. A method of inhibiting corrosion of a capillarystring or an umbilical tubing made up of stainless steel or a corrosionresistant alloy, the method comprising: introducing an organic chemicalblend additive to a production well through the capillary string or theumbilical tubing, where the organic chemical blend additive comprises: anitrate, a maleic acid copolymer, an organic solvent in an amountgreater than 50 wt. %, based on a total amount of the organic chemicalblend additive, and less than 10 wt. % water, based on a total amount ofthe organic chemical blend additive; and the organic chemical blendadditive inhibiting corrosion of the capillary string or the umbilicaltubing.
 2. The method of claim 1, comprising the further step ofinhibiting localized corrosion of the stainless steel or corrosionresistant alloy surface of the conduit.
 3. The method of claim 1,comprising the further step of improving the repassivation potential ofthe stainless steel or corrosion resistant alloy surface of the conduit.4. The method of claim 1, wherein nitrate is selected from a groupconsisting of calcium nitrate, sodium nitrate, potassium nitrate, and acombination thereof.
 5. The method of claim 1, wherein the maleic acidcopolymer is a polycarboxylic acid having the following chemicaldescription: propenoic acid, ethyl ester, polymer with ethenyl acetateand 2,5 furandione, hydrolyzed.
 6. The method of claim 1, wherein theorganic chemical blend additive further comprises an imidazoline.
 7. Themethod of claim 1, wherein the nitrate is in solution form and presentin the organic chemical blend additive in an amount less than 2 wt. %,based on the total amount of the organic chemical blend additive.
 8. Amethod of inhibiting corrosion of a capillary string or an umbilicaltubing made up of stainless steel or a corrosion resistant alloy, themethod comprising: introducing an organic chemical blend additive to aproduction well through the capillary string or the umbilical tubingmade up of stainless steel or a corrosion resistant alloy, where theorganic chemical blend additive comprises: a nitrate, a maleic acidcopolymer, an organic solvent in an amount greater than 50 wt. %, basedon a total amount of the organic chemical blend additive, and less than10 wt. % water, based on a total amount of the organic chemical blendadditive; and the organic chemical blend additive inhibiting corrosionof and improving repassivation potential of the capillary string or theumbilical tubing; where inhibiting localized corrosion of the stainlesssteel or corrosion resistant alloy surface of the conduit and improvingthe repassivation potential of the stainless steel or corrosionresistant alloy surface of the conduit is improved synergistically ascompared with an otherwise identical organic chemical blend additiveabsent either the nitrate or the maleic acid copolymer.
 9. The method ofclaim 8, wherein nitrate is selected from a group consisting of calciumnitrate, sodium nitrate, potassium nitrate, and a combination thereof.10. The method of claim 8, wherein the maleic acid copolymer is apolycarboxylic acid having the following chemical description: propenoicacid, ethyl ester, polymer with ethenyl acetate and 2,5 furandione,hydrolyzed.
 11. The method of claim 8, wherein the organic chemicalblend additive further comprises an imidazoline, where inhibitinglocalized corrosion of the stainless steel or corrosion resistant alloysurface of the conduit and improving the repassivation potential of thestainless steel or corrosion resistant alloy surface of the conduit isimproved synergistically as compared with an otherwise identical organicchemical blend additive absent either: the nitrate and the maleic acidcopolymer, or the imidazoline.
 12. The method of claim 8, wherein thenitrate is in solution form and present in the organic chemical blendadditive in an amount less than 2 wt. %, based on the total amount ofthe organic chemical blend additive.
 13. A method of inhibitingcorrosion of a capillary string or an umbilical tubing made up ofstainless steel or a corrosion resistant alloy, the method comprising:introducing an organic chemical blend additive to a production wellthrough the capillary string or the umbilical tubing made up ofstainless steel or a corrosion resistant alloy, where the organicchemical blend additive comprises: a nitrate, a maleic acid copolymer,an organic solvent in an amount greater than 50 wt. %, based on a totalamount of the organic chemical blend additive, and less than 10 wt. %water, based on a total amount of the organic chemical blend additive;and the organic chemical blend additive inhibiting corrosion of thecapillary string or the umbilical tubing; where all components of theorganic chemical blend additive are in solution.
 14. The method of claim13, comprising the further step of inhibiting localized corrosion of thestainless steel or corrosion resistant alloy surface of the conduit. 15.The method of claim 13, comprising the further step of improving therepassivation potential of the stainless steel or corrosion resistantalloy surface of the conduit.
 16. The method of claim 13, whereinnitrate is selected from a group consisting of calcium nitrate, sodiumnitrate, potassium nitrate, and a combination thereof.
 17. The method ofclaim 13, wherein the maleic acid copolymer is a polycarboxylic acidhaving the following chemical description: propenoic acid, ethyl ester,polymer with ethenyl acetate and 2,5 furandione, hydrolyzed.
 18. Themethod of claim 13, wherein the organic chemical blend additive furthercomprises an imidazoline.
 19. The method of claim 13, wherein thenitrate is in solution form and present in the organic chemical blendadditive in an amount less than 2 wt. %, based on the total amount ofthe organic chemical blend additive.